Process for the production of lactams



. PROCESS FOR THE PRODUCTION OF LACTAMS Wallace F. Runge, Terre Haute, Ind., assignor to Commercial Solvents Corporation, New York, N.Y., a corporation of Maryland No Drawing. Filed May '13, 1959, Ser. No. 812,786

5 Claims. (Cl. 260-2393) My invention relates to the production of lactams, and more particularly, to a process for the production of lactams by the Beckmann rearrangement of cyclic ketoximes using fuming sulfuric acid.

The conversion of oximes of acyclic or cyclic ketones by treatment with sulfuric acid into cyclic lactams is well known, this reaction being generally known as the Beckmann transformation, or rearrangement. Many modifications of this reaction have been tried, but most of them have been found to be impractical or uneconomical from a commercial point of view for various reasons. Practical application of this reaction requires that the operation be carried out economically; that is, with high conversions and yields and with the production of the cyclic lactams in a form easily recoverable in a relatively high state of purity. This is particularly the case in the production of caprolactam from cyclohexanone oxime, probably the v United States Patent anone oxime, ethyl-cyclohexanone oxime, 1,1,Ii-dimethylcyclohexanone oxime, 1,1,4-trimethyl-cyclohexanone' ox.- 1 ime, 1,2,4-trimethyl-cyclohexanone oxime, and heptanone oxime. To effect the Beckmann rearrangement of the. above ketoximes into the corresponding cyclic lactams, bymy improved process, it is necessary to use sulfuricacid in concentration of not less than 99%, sulfuric acid. I find it preferable to use 100% concentration sulfuric acid and fuming sulfuric acid containing S0 in concentrations I ranging from 1 to 10%. I have found that the use of fuming sulfuric acid of substantially higher concentra- I tions lead to generally unsatisfactory results. While, therefore, I can add to my reaction mixture fuming sulfuric acid: containing S0 of concentrations higher than10%",

it is important for most desirable results'that the final my process determines to a large extent the temperatures time in order to complete the Beckmann rearrangement than when higher concentration sulfuric acid, suchY'as fuming sulfuric acid, are employed. Using 99% concentration acid, little or no reaction takes place at room temperature over fairly extended periods of time. When,

most important application of this reaction from a cOm- Y mercial point of View.

The use of dilute sulfuric acid has been found generally unsuitable because of the undesirable effects from the presence of the water in the dilute sulfuric acid. Numerous attempts have been made to use concentrated and a I ment be carried out in the presence of various organic.

compounds inert to sulfuric acid. This process-also has been found to be disadvantageous because of the difliculty in selecting suitable compounds which are not affected by the sulfuric acidunder the conditions of the rearrangement aswell as thedifliculty of separating the last traces of these compounds from the cyclic lactam. 7

My new and improved process for effecting the Beckmann rearrangement of cyclic ketoximes into cyclic lactams overcomes the variousoperating difliculties'experienced in previous processes and at the same time gives high yields of the desired cyclic lactams in a form readily recoverable in the degree of purity required for products such as caprolactam to be-used in the production of synthetic fibers.

My process is applicable generally to the Beckmann rearrangement of oximes of acyclic or. cyclic ketones. Among the ketoximes which can be satisfactorily treated according to my improved process may be mentioned the following, but it is understood of course that the process is not limited specifically to these particular compounds: methyl-cyclopropanone oxime, methyl-cyclobutanone oxime, cyclopentanone oxime, l-methyl-cyclopentanone oxime, l-ethyl-cyclopentanone oxime, 1,1-dimethyl-cyclopentanone oxime, 1-methyl-2-ethyl-cyclopentanone oxime, 1,1,2 trimethyl cyclopentanone oxime, 1,1,3 trimethylcyclopentanone oxime, cyclohexanone oxime, l-methylcyclohexanone oxime, 1,l-dimethyl-cyclohexanone oxime, 1,3f-dimethyl-cyclohexanone oxime, 1,4-dimethyl-cyc1ohexa however, the concentration is raised to 100% sulfuric acid, satisfactory yields are obtained at room temperature over a period of 8l0 hours. When the concentration is raised to say fuming sulfuric acid containing 1 to 5% 503 the mixing of the ketoxime with the fuming sulfuric acid must be effected under carefully controlled conditions with sufficient cooling to maintain the mixture ibelow approximately C.'untilthe reactants are completely mixed, after which the mixture is raised to a'tempera-. ture of not substantially in excess of 70 C., and prefer-r ably 4060 C., and maintainedat this temperature for periods of time ranging froml hours at 60 C. to4" hours at 40 C. 1 I

As" indicated above, I can carry out the Beckmann're arrangement reaction by my improved process at either relatively low or at elevated temperatures byfichanging' the concentration of the acid. I can, for exa'mple,:carry out my improved process by dissolving the ketoxirne "in sulfuric acid of 100% strength or higher at temperatures:

below 50 C., and allowing the reaction to takeplacef at;

temperatures ranging from 40-60 C. Using 100% gacid,

the reaction is quite slow (8 hours) and gives yields and product quality comparable to those obtained at elevated temperatures. When fuming sulfuric acid 1%; 2%; 4.5% .50 is used, significantly higher yields are 011-:

' tained with a slight improvementin product quality; The;

with'somewhat less satisfactory results by simultaneously.

adding the ketoxime, preferably in molten form, and the;

sulfuric acid of desired concentration in separate streams;

into a reaction vessel at ratesso asto .give the'desired ratio of ketoxime to sulfuric acid. By maintaining the temperature of the reaction mixture at -130 Cfand continuously withdrawing reaction mixture fromthey sel at a rate so as to maintain a residence time thereinfo quality are obtained. 1 I, I

,Amodification of the above two procedures'consists '91 2,976,222,? Patented Mar. 21,

10-30 minutes, satisfactory results, both" as to yield first mixing the ketoxime and 99% sulfuric acid in the required proportions while maintaining the temperature of the mixture at not in excess of 50 C. The resulting mixture is then continuously introduced into a separate vessel simultaneously with an amount of fuming sulfuric acid sufiicient to give in the reaction mixture a final concentration of sulfuric acid containing 1 to 10% S and, preferably, 2 to 4% S0 The temperature of this resulting mixture of ketoxime and fuming sulfuric acid is maintained at a temperature ranging from 40 to 70 C. and material is removed at a rate such that the total reaction mixture is maintained approximately constant and a residence time of 1 to 5 hours is obtained. At a temperature of 60 C., a residence time of approximately two hours gives satisfactory results.

Mole ratios ranging from 1 mole of ketoxime to 3.0 moles of sulfuric acid give good results in my process. I prefer to use mole-ratios within the range 1.0 to 1.5 H SO 1.0 oxime.

A better understanding of the nature of my invention can be had by reference to the following examples which illustrate my invention. I do not intend, however, to be limited to the particular ketoxime, procedures, amounts and conditions set forth therein, but I intend for the equivalents and variations obvious to those skilled in the art to be included within the scope of this specification and the attached claims.

Example I To 719 g. (7.26 moles) 99% sulfuric acid was added 373 g. (3.3 moles) of powdered cyclohexanone oxime while holding the temperature of the resulting mixture below 30 C. with vigorous agitation and cooling, when necessary. The resulting mixture was then added at a rate of about mls. per minute to a reactor consisting of a 500 ml., 4-necked round bottom flask with drain cock in the bottom and provision for heating and cooling, and fitted with a mechanical agitator, two dropping funnels and a thermometer and containing 145 g. of 34.2% caprolactam in 99% sulfuric acid heated to a temperature of 115 C. A total of 1073 g. of the reaction mixture was added to the reactor while withdrawing reaction mixture from the bottom thereof at a rate so as to keep a constant level of liquid in the reactor. During the reaction period of 75 minutes, the temperature range was maintained at 120-125 C. and reaction mixture was removed at the rate of approximately 9.5 ml. per minute, giving a residence time of approximately 10.5 minutes for the reaction mixture in the reactor. A total of 1216 g. of a very light colored crude reaction product was obtained. This crude reaction product was then slowly added to 1 to 4 volumes of saturated aqueous ammonium sulfate solution simultaneously with gaseous ammonia at a rate such that the pH was held between 7 and 8 and the temperature below 40 C. After neutralization, the precipitated ammonium sulfate was removed by centrifugation and the filtrate allowed to separate into layers. The aqueous layer was removed and used for subsequent neutralizations. Upon distillation under reduced pressure the upper oil layer gave 69% crude caprolactam, 29% water and 2% undistillable residue. This amounted to a 94% yield of crude caprolactam containing 0.14% oxime, 68 p.p.m. volatile base and having a permanganate requirement of 0.3% (i.e., the amount of potassium permanganate required in the treatment of crude caprolactam to enable it to pass permanganate time specification).

The crude product obtained as above described was next treated in the form of a 25% aqueous solution with the required amount of potassium permanganate, filtered, subjected to deionization, and the water then removed by distillation under reduced pressure followed by reflux at 165 C. and 30 mm. to remove volatile base. Distillation at reduced pressure then gave specification grade caprolactam (caprolactam containing no more than 0.0025% oxime, and 25 p.p.m. volatile base).

Example H To 484 g. (4.95 moles) fuming sulfuric acid containing 2.08% 50;, was added 3.73 g. (3.3 moles) cyclohexanone oxime over a period of minutes while maintaining the temperature of the resulting mixture at about 30 C. After the addition was complete, the mixture was maintained for an additional 30 minutes at a temperature of 35-40 C. in order to complete solution of the oxime. After complete solution, the reaction mixture was maintained at a temperature of 35-37 C. for an additional period of 3 /2 hours. The resulting reaction mixture was treated as described in Example I. A 95% yield of crude caprolactam having a permanganate requirement of 0.04%, containing no unconverted oxime and only 36 p.p.m. of volatile base was obtained.

Example Ill To 350 g. 99% sulfuric acid was added 378 g. of powdered cyclohexanone oxime over a period of 40 minutes while holding the temperature at about 30 C. The resulting mixture was stirred for an additional two hours while maintaining the temperature at 3035 C. in order to complete solution of the oxime. To the resulting solution was then added 134 g. fuming sulfuric acid containing 20% S0 dropwise over a period of 40 minutes while holding the temperature at about 20-25" C. during the first 30 minutes and then permitting the temperature to rise to 40 C. The resulting mixture was then allowed to stand at a temperature of 40 C. for a period of 3 /2 hours after which is was neutralized as described in Example I with ammonium sulfate solution to a final pH of 7.5. The resulting oil was isolated and distilled to yield a 93.6% crude caprolactam having a permanganate requirement of 0.03% and containing 0.001% oxime, and 34 p.p.m. volatile base.

Example IV The reactor described in Example I was charged with 142 g. of 34.2% caprolactam in 99% sulfuric acid and the mixture heated to C. To the heated mixture was then simultaneously added through separate dropping funnels 339 g. (3.0 moles) molten cyclohexanone oxime and 445 g. (4.5 moles) 99% sulfuric acid. The temperature of the reaction mixture was maintained at 115-125 C. during the period of the addition which lasted 80 minutes. The reaction product was removed from the bottom of the reaction vessel at the rate of approximately 7.5 ml. per minute, thus giving a residence time of approximately 13.4 minutes. A total reaction product of 924 g. was obtained, neutralized, and treated as described in Example I. A 91% yield of crude capro' lactam having a permanganate requirement of 0.6% and containing 0.34% oxime and 91 p.p.m. volatile base was obtained.

Example V To 350 g. (3.325 moles) 99% sulfuric acid was added 373 g. (3.3 moles) powdered cyclohexanone oxime over a period of approximately 90 minutes while maintaining the temperature at approximately 30 C. while stirring the mixture until solution was complete. The reactor described in Example I was charged with 268 g. of a 42% solution of caprolactam in fuming sulfuric acid containing 2.44% S0 This mixture was heated to 60 C. and the solution of cyclohexanone oxime in 99% sulfuric acid prepared as above described was added at a rate of about 1.4 ml. per minute to the heated solution in the reactor simultaneously with g. fuming sulfuric acid containing 17% S0 at a rate of approximately 0.25 ml. per minute. A total of 10 ml. of feed mix was added before beginning removal of reaction mixture. from the bottom of the reactor and this level acid and permitting the resulting mixture to react at temperatures ranging from about 40 to about 70 C.-

3. In a process for the production of lactams from cyclic ketoximes selected from the group consisting of cyclo-aliphatic ketoximes and alkyl substituted cycloaliphatic ketoximes, the cyclealiphatic portion of the ketoxime containing from 3 to 7 carbon atoms inclusive, the steps which comprise continuously mixing the cyclic ketoxime in molten form with sulfuric acidhaving a concentration of from about 99 to about 105% sulfuric acid, said cyclic ketoxime and said sulfuric acid'being' mixed at a ratio of 1 mole of cyclic ketoxime to 1 to 3.0

M01 Ratio, Temp, Time Yield, Perm. Oxime, Volatile Cone. of Acid Acid to 0. ReqcL, Percent Req., Percent Base,

Oxime hrs Percent p.p.m.

1. 5 to 1.0 40 8 91 0.05 0.005 53 1. 5 to 1.0 40 5 97 0.05 0.001 32 1. 5 to 1.0 40 2% 95. 2 0.01 0.001 21 1.1 to 1.0 115-125 16. 0 89 4. 8 1. 94 168 1. 3 to 1.0 115-125 1 13. 2 87. 6 2. 2 0.95 172 1. 65 to 1.0 115-125 1 14. 0 91. 5 2.0 0.86 168 2. 2 to 1.0 115-125 11.0 90. 5 0.8 0.37 157 1. 5 to 1.0 115-125 13. 0 81 17. 5 11.92 549 1. 5 to 1.0 115-125 1 12. 6 91. 5 0.01 r 0.046 32 1. 5 to 1.0 115-125 11. 9 91. 5 0.07 0. 004 66 S03 1. 5 to 1. 0 115-125 15. 5 84. 7 0.01 0.02 137 1 Minutes.

Examination of the results reported above shows that my improved process gives high yields of caprolactam of degree of purity close to that required for use in the production of synthetic fibers. This markedly simplifies any final purification required to give a salable product. In fact, the crude oil obtained when my process is carried out at low temperatures is of such high quality the distillation of the crude oil to give crude caprolactam can usually be eliminated, thus saving operational time and cost and increasing the overall yield.

Now having described my invention, What I claim is:

1. In a process for the production of lactams from cyclic ketoxirncs selected from the group consisting of cycle-aliphatic ketoximes and alkyl substituted cycle-aliphatic ketoxirnes, the cyclo-aliphatic portion of the ketoxime containing from 3 to 7 carbon atoms inclusive, the steps which comprise dissolving the cyclic ketoxime in sulfuric acid having a concentration of from about 99 to about 105% sulfuric acid at a temperature ranging from about 40 to about 60 C. in a ratio of 1 mole of said cyclic ketoxime to 1 to 3.0 moles of said sulfuric acid and permitting said mixture to react at temperatures ranging from about 40 to about 70 C.

2. In a process for the production of lactams from cyclic ketoximes selected from the group consisting of cycle-aliphatic ketoximes and alkyl substituted cycloaliphatic ketoximes the cycle-aliphatic portion of the ketoxime containing from 3 to 7 carbon atoms inelusive, the steps which comprise dissolving the cyclic ketoxime in sulfuric acidhaving a concentration of from about 99 to about 104% sulfuric acid at a temperature from about 40 to about 60 C. in a ratio of 1 mole of said cyclic ketoxime to 1 to 3.0 moles of said sulfuric acid, adding to the resulting mixture sulfuric acid having a S0 concentration of from about 1 to about 10% in amounts such that the final concentration of sulfuric acid ranges from about 100 to about 105% sulfuric moles of said sulfuric acid and at a temperature ranging from about 40 to about 60 C. and permitting said mixture to react at temperatures ranging from about 40 to about C.

4. In a process for the production of lactams from cyclic ketoximes selected from the group consisting of cycle-aliphatic ketoximes and alkyl substituted cycloaliphatic ketoximes, the .cyclo-aliphatic portion of the .ketoxime containing from 3 to 7 carbon atoms inclusive,

the steps which comprise continuously mixing the said cyclic ketoxime in molten form with sulfuric acid having a concentration of from about 99 to about 10 4% sulfuric acid in a ratio of 1 mole of cyclic ketoxime to 1 to 3.0 moles of said sulfuric acid at a temperatureranging from about 40 to about 60 C. and adding the resulting solution to a separate vessel simultaneously and co-ordinated with the addition thereto of sulfuric acid having a content ranging from about 1 to about 10%, the amounts of said sulfuric acid addition being regulated to give a final sulfuric acid concentration of from about 100 to about sulfuric acid and a final quantity of sulfuric acid equal to 1 to 3.0 moles of sulfuric acid for each mole of cyclic ketoxime and permitting the reaction mixture to react at temperatures ranging from about 40 to about 70 C.

5. The process of claim 4 wherein the reaction is conducted at a temperature ranging from about 40 to about 70 C. for a period of from about 1 to about 5 hours.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS FOR THE PRODUCTION OF LACTRAMS FROM CYCLIC KETOXIMES SELECTED FROM THE GROUP CONSISTING OF CYCLO-ALIPHATIC KETOXIMES AND ALKYL SUBSTITUTED CYCLO-ALIPHATIC KETOXIMES, THE CYCLO-ALIPHATIC PORTION OF THE KETOXIME CONTAINING FROM 3 TO 7 CARBON ATOMS INCLUSIVE, THE STEPS WHICH COMPRISE DISSOLVING THE CYCLIC KETOXIME IN SULFURIC ACID HAVING A CONCENTRATION OF FROM ABOUT 99 TO ABOUT 105% SULFURIC ACID AT A TEMPERATURE RANGING FROM ABOUT 40* TO ABOUT 60*C. IN A RATIO OF 1 MOLE OF SAID CYCLIE KETOXIME TO 1 TO 3.0 MOLES OF SAID SULFURIC ACID AND PERMITTING SAID MIXTURE TO REACT AT TEMPERATURES RANGING FROM ABOUT 40* TO ABOUT 70*C. 